Quantification of ice production in Laptev Sea polynyas and its sensitivity to thin-ice parameterizations in a regional climate model

Oliver Gutjahr,Clemens Drüe,Andreas Preußer,Günther Heinemann,Sascha Willmes

doi:10.5194/tc-10-2999-2016

Abstract

Abstract. The quantification of sea-ice production in the Laptev Sea polynyas is important for the Arctic sea-ice budget and the heat loss to the atmosphere. We estimated the ice production for the winter season 2007/2008 (November–April) based on simulations with the regional climate model COSMO-CLM at a horizontal resolution of 5 km and compared it to remote sensing estimates. A reference and five sensitivity simulations were performed with different assumptions on grid-scale and subgrid-scale ice thickness considered within polynyas, using a tile approach for fractional sea ice. In addition, the impact of heat loss on the atmospheric boundary layer was investigated. About 29.1 km3 of total winter ice production was estimated for the reference simulation, which varies by up to +124 % depending on the thin-ice assumptions. For the most realistic assumptions based on remote sensing of ice thickness the ice production increases by +39 %. The use of the tile approach enlarges the area and enhances the magnitude of the heat loss from polynyas up to +110 % if subgrid-scale open water is assumed and by +20 % for realistic assumptions. This enhanced heat loss causes in turn higher ice production rates and stronger impact on the atmospheric boundary layer structure over the polynyas. The study shows that ice production is highly sensitive to the thin-ice parameterizations for fractional sea-ice cover. In summary, realistic ice production estimates could be retrieved from our simulations. Neglecting subgrid-scale energy fluxes might considerably underestimate the ice production in coastal polynyas, such as in the Laptev Sea, with possible consequences on the Arctic sea-ice budget.

Highlights

The rate of sea-ice growth strongly depends on the energy fluxes at the ice or ocean surface
In this study we quantified the ice production in the Laptev Sea polynyas for the winter 2007/2008 based on simulations with a regional atmospheric model (CCLM) and remote sensing data
The results show that the ice production is highly sensitive to the assumptions made on the ice thickness within polynyas

Summary

Introduction

The rate of sea-ice growth strongly depends on the energy fluxes at the ice or ocean surface. If the total atmospheric heat flux is negative, the ocean loses heat either directly to the atmosphere or via conduction through an existing sea-ice cover. In the former case frazil ice forms, which aggregates subsequently to a new thin-ice layer under calm conditions. In the latter case basal freezing occurs to balance this heat loss. Most of the heat loss from the ocean occurs over open water or thin-ice areas, such as leads and polynyas, within an otherwise compact sea-ice cover (Smith et al, 1990; Morales Maqueda et al, 2004). The fraction of such areas in polar oceans is relatively small during winter, they are of major importance for the heat budget of the atmospheric boundary layer (ABL) (Heinemann and Rose, 1990; Haid et al, 2015) and the ocean circulation, such as the Arctic circumpolar boundary current (e.g. Aksenov et al, 2011; Rudels et al, 1999)

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